Measurement of Interstellar Polarization and Estimation of Galactic Extinction for the Direction of X-ray Black Hole Binary V404 Cygni

Abstract

V404 Cygni is a well-known black hole binary candidate thought to have relativistic jets. It showed extreme outbursts on June 2015, characterized by a large amplitude and short time variation of flux in the radio, optical, and X-ray bands. Not only disk emission, but also synchrotron radiation from the relativistic jets were suggested by radio observations. However, it is difficult to measure the accurate spectral shape in the optical/near infrared band because there are uncertainties of interstellar extinction. To estimate the extinction value for V404 Cygni, we performed photopolarimetric and spectroscopic observations of V404 Cygni and nearby field stars. Here, we estimate the Galactic extinction using interstellar polarization based on the observation that the origin of the optical polarization is the interstellar medium, and investigate the properties of interstellar polarization around V404~Cygni. We found a good correlation between the color excess and polarization degree in the field stars. We also confirmed that the wavelength dependence of the polarization degree in the highly polarized field stars was similar to that of V404~Cygni. Using the highly polarized field stars, we estimated the color excess and the extinction, $E(B-V)=1.2\pm 0.2$ and $3.0<A(V)<3.6$, respectively. A tendency for a bluer peak of polarization (${\lambda }_{\max }<5500$ Å) was commonly seen in the highly polarized field stars, suggesting that the dust grains toward this region are generally smaller than the Galactic average. The corrected spectral energy distribution of V404~Cygni in the near infrared (NIR) and optical bands in our results indicated a spectral break between $2.5\times 10^{14}$ Hz and $3.7\times 10^{14}$ Hz, which might be originated in the synchrotron self absorption.

11 pages, 6 figures, 3 tables. Accepted for publication in PASJ

References in corpus (6)

• Repetitive Patterns in Rapid Optical Variations in the Nearby Black-hole Binary V404 Cygni
• Optical and Near-Infrared Polarimetry of Highly Reddened Type Ia Supernova 2014J: Peculiar Properties of Dust in M82
• The first polarimetric signatures of infrared jets in X-ray binaries
• Time-resolved optical/near-IR polarimetry of V404 Cyg during its 2015 outburst
• Modelling interstellar extinction and polarization with spheroidal grains
• MASTER optical polarization variability detection in the Microquasar V404 Cyg/GS2023+33

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• Optical polarization signatures of black hole X-ray binaries
• Follow-up Observations for IceCube-170922A: Detection of Rapid Near-Infrared Variability and Intensive Monitoring of TXS 0506+056